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A simple and practical method designed to measure abnormal concentrations of plasma formate is described. The method uses formate dehydrogenase and a color reagent to produce a stable formazan color. The method requires no deproteinization and has a one-point standard calibration. The precision at 1.0 and 5.0 mmol/L formate is 2.9% and 1.7% within-day and 5.5% and 2.3% between-day. Recovery averages 100% for formate concentrations of 2.0 to 10.0 mmol/L. The proposed method is inexpensive, robust, and suitable for routine use and shares the color reagent used for the assay of plasma lactate and 3-hydroxybutyrate, both important analytes in metabolic acidosis.

Nineteen patient blood samples each with modified hematocrit concentrations of approximately 20, 30, 40, 50, and 60%, were assayed for their glucose concentration by the Glucometer II. Blood removal from the test strip was by the one- and two-blot techniques. The reference method was the Yellow Springs Instruments (YSI) blood glucose analyzer. Glucometer II results were falsely high for the single blot (13-59%, mean 33%) and double blot (12-41%, mean 19%) at 20% hematocrit and falsely low at 60% hematocrit for the single blot (22-44%, mean 37%) and the double blot (26-49%, mean 43%). At 40-50% hematocrit, Glucometer II and YSI results agreed only for the one-blot technique.

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In the kinetic angiotensin-converting enzyme (ACE) method, a practical and optimal buffer is 80 mmol/L borate buffer at pH 8.2 (37 degrees C). A lag phase is detected in the reaction, and a 5-min incubation of substrate and plasma is suggested before the kinetic measurement. The substrate, N-[3-(2-furyl)acryloyl]-L-phenylalanylglycylglycine (FAPGG), concentration is maximized at 1.0 mmol/L and the measurement wavelength is at 345 nm to ensure linearity of measurement. The proposed procedure uses a 1:9 plasma-to-reagent volume ratio. The linear range of the assay extends to approximately 170 U/L, representing a 25% substrate hydrolysis. The FAPGG absorptivity is determined by measuring the difference in absorbance between 1.0 mmol/L FAPGG and the product solutions. The wavelength fidelity is checked by noting the expected absorbance value of the FAPGG solution, and a 1.0-nm deviation from 345 nm alters the absorbance by 15.5%. The precision of ACE assays at approximately 60 and 100 U/L is 3.5% and 2.4% within batch and 2.9% and 2.6% between batch, respectively. The reference interval (2.5th to 97.5th percentiles) is 41-139 U/L, and there is no difference between values for men and women.

We report another patient with a circulating alkaline phosphatase/immunoglobulin complex in his blood, and describe a simple method of demonstrating such complexes. On electrophoresis on cellulose acetate, the complex was relatively slow moving and there was no activity in the normal bone/liver isoenzyme region. When the serum was treated with trypsin, the slow band disappeared and the normal pattern was restored.

For this direct colorimetry of urinary oxalate, commercially available oxalate oxidase (EC 1.2.3.4) is used. The urine is first diluted, to diminish the effect of interfering substances. Analytical recovery of oxalate from urines with five different oxalate concentrations (0.4 to 2.0 mmol/L) ranged from 92 to 109% (mean 99%). The within-day and between-day precision (CV) of the method for a wide range of oxalate concentrations averaged better than 10%. There is good correlation (r = 0.977) between this enzymatic method (y) and the chemical method of Hodgkinson and Williams (x) [Clin Chim Acta 36: 127-132, 1972], the regression equation being y = 1.014x + 0.061. Urines with added ascorbate give falsely increased results. The proposed method is inexpensive and simple to perform.

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